Sunday 20 December 2020

Oil Pumps

From pictures of the bike in its original naturally-aspirated form it is evident that there is only one oil pump – the standard AJS reciprocating oil pump for both feed and scavenge. This had proved quite adequate on the single cylinder OHC engines and, at this stage, there are no cambox scavenge pumps.

However, in later pictures and after the supercharger was fitted, individual cambox scavenge pumps driven from the camshafts have appeared. This is clearly seen in the picture below that I took of the bike as it is today in the National Motorcycle Museum.

It can also be seen that the original AJS reciprocating pump has been replaced by a gear-type pump. Reciprocating pumps deliver oil at a relatively low pressure and low flow rate so it was probably considered a sensible upgrade to provide better lubrication for a 1000cc engine that was intended to power a bike at over 130 mph!

Cambox lubrication can be a problem: the problem is not getting oil into the cambox but rather getting it out and back into the engine. AJS ended up fitting a scavenge pump on the (other) end of the camshaft in the single cylinder OHC engines after 1930 and Velocette had done this from the early days of the KTT. I had previously had plenty of problems with cambox lubrication with the AJcette engine  and I had decided at the outset of the V-Twin project that I would fit cambox scavenge pumps.

But, what pumps to fit? At the last autojumble I attended (Shepton Mallet in March 2020), I happened to stumble across a collection of vintage Sunbeam gear pumps, 3 in fact, for which the bodies were completely useless but the gears were in good condition. I chose the best sets of gears and made new steel bodies for 2 complete identical pumps. One advantage of using a gear pump is that they are self priming however they do need to operate with minimal clearances to avoid leakage reducing their efficiency. An end-mill was made specifically to machine the 2 main holes for the pump gears.


Housings were then made for both pumps from 6082 T6 aluminium and each pump was located within its respective housing using the aluminium plates previously set up with a reference hole aligned with the camshaft to position the pump drive (see previous blog).

The picture below shows one of the pumps within its housing and machining part of the flange for fixing to the timing case.


The picture below shows the completed pumps and housings.

When the pumps are “plumbed in” later in the project, the upstream side will take oil from various gutters in the Velocette cambox and the downstream connection will feed the scavenged oil into its side of the timing case.

The last oil pump to be fitted is the main feed/scavenge pump for the engine which is driven from the end of the camshaft drive shaft for the chain drive. Here, the same Velocette gear pump as has been previously installed in the AJcette engine (part# K79/2 from GroveClassics) was used. There is one small modification that needs to be made to this pump before it can used here, namely to “blank off” the slot in the flange at the end of the pump and which normally feeds oil directly into the engine, shown below at the top of the picture.

The oil feed into this engine is quite different from the Velocette; here it is fed from a copper pipe from the oil pump to the drive side of the engine and through a succession of drillings in the crankcase and crankshaft to the big end. The camboxes are fed from 2 further pipes into the top of the each cambox. Excess oil is dumped directly into the crankcase.

The pump end-cap was brazed and then machined back to round.

A flange, to which the pump was attached, and a pump body were then machined to support the pump

The main oil pump and the 2 cambox scavenge pumps could then be secured to the timing case and mounted on the engine.


With a set of brass connectors


installation of the main oil pump was complete.

The last part of the installation was to make the connecting pieces to drive the oil pumps. But before these could be machined it was necessary to make a gasket for the outer-to-inner timing case as this affects the length of the connecting pieces.


The connecting pieces were then made from silver steel and the recess at the end of each was spark eroded.


After hardening/tempering the connectors, the complete set of pumps and their drives was now ready for mounting on the engine.